PARIS/NEW YORK Europe's Airbus is considering whether to drop lithium-ion batteries and switch back to traditional ones on its A350 passenger jet as investigators probe Boeing 787 safety incidents, several people familiar with the matter said.

The move comes amid a wider rethink in the aerospace industry on whether the powerful but delicate backup energy systems are technically "mature", or predictable, they said.

Industry executives, insurers and safety officials told Reuters the technology's predictability was being questioned at senior levels as investigators struggle to find the cause of incidents that led to the grounding of Boeing's 787 Dreamliner.

"There is an increasing doubt over the technology," said a person familiar with industry-wide discussions on the issue. "It may well be the future but for now it is a question of maturity. The information on the two incidents is not reassuring."

The U.S. National Transportation Safety Board, which is examining a fire on a 787 at Boston airport a month ago, said on Thursday it had identified where the fire broke out but not the cause. A similar investigation is under way in Japan.

A spokesman for EADS unit Airbus said it would study the outcome of the U.S. probe: "Let's not get ahead of ourselves. There are no conclusions by the NTSB yet and the investigation is still ongoing." All options are open, he added.

France's Saft, which makes both the new and old batteries for Airbus, did not respond to requests for comment. Last month it insisted lithium-ion was safe.

The A350 would be the second large passenger jet to fly on lithium-ion batteries for backup electrical power after the Dreamliner, which pioneered their use in passenger transport to support an increasing array of electrical systems.

Airbus said last week it had a plan B for its battery and time to respond to any rule changes.

However, industry sources said that following the NTSB's latest comments, the odds are shortening that Airbus will switch to nickel-cadmium technology used on jets like the A380.

"It is a classic risk-management problem. If you don't know the cause of something you can't quantify the risk that it will happen again," an international safety official told Reuters.

"In that case, you have little choice but to take a temporary step back and rely on something better understood."

INSURERS CAUTIOUS

Experts say that if the 787 probe fails to provide clear answers soon, pressure may build for Airbus to pre-empt the findings and switch solutions to head off development risk.

Airbus plans an A350 maiden flight in mid-year, followed by a year of flight trials and certification, during which the distraction of re-engineering could increase the risk of delays.

The A350 is due to be delivered in the second half of 2014, around two years behind its original schedule.

Reverting to nickel-cadmium would mean sacrificing the lighter weight of lithium-ion, equivalent on the A350 to one adult male passenger out of between 270 and 350 passengers.

"The penalty in weight compared with the risks associated with 'li-ion' is minimal," said Nick Cunningham, an aerospace analyst at Agency Partners in London.

Boeing declined to say whether it was looking at making the same switch to restore its fleet to service. "We're simply focused on resolving the issue, working closely with regulatory and investigative authorities," a spokesman said.

Boeing said the U.S. planemaker had selected lithium-ion batteries because they best met the performance and design objectives of the 787. "Nothing we learned during the design of the 787 or since has led us to change our fundamental assessment of the technology," the company said.

Because of its highly electric design, replacing many hydraulic systems, the 787 consumes more power than the A350.

Plane and battery makers say lithium-ion is safe but recognize it is in the early stages of use in commercial flying.

Cunningham said Airbus and Boeing had learned from past development snags that it pays to tackle problems early rather than having to embark on costly refits that burn up cash.

Insurers too are taking a more cautious approach to lithium-ion batteries, warning underwriters to consider the risks more closely in a way that could mean higher prices for airlines.

Global Aerospace, the London-based pool that acts as Boeing's lead insurer, has already said the planemaker has coverage for groundings and compensation.

The question is what it will cost others in the future to get the same kind of coverage, or any coverage for that matter where the volatile battery technology is involved.

A senior U.S. insurance executive, asked how the Boeing 787 incidents would affect the ability of others to be insured, said: "it's just a question of price."

At least two major insurers are communicating with staff about the science behind lithium-ion, the risks associated with its use and the caution they should take in writing policies.

Lithium-ion batteries have been on the insurance industry's radar for quite some time. The industry's biggest fear has been the costs when batteries are stored in bulk and one catches fire, leading to a conflagration that destroys inventories.

"The industry maybe never thought this was going to end up in an airliner," the insurance executive said.

The Fire Protection Research Foundation gathered members in Baltimore in August 2011 to discuss lithium-ion safety risks, a meeting well attended by some of the largest U.S. property insurers.

Their conclusion, at the time, was that more study needed to be conducted on packaging design and the most effective fire-suppression technologies, some of the same issues now being considered by aviation regulators in their Boeing probe.

The meeting's aviation workgroup specifically noted that one of the issues to consider was "fire in flight", according to minutes of the proceedings seen by Reuters.

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